Roofing contractors use a variety of fall arrest systems to protect their workers from falls. It is also preferable that these carts meet Occupational Safety and Health Administration (OSHA) requirements. In many applications, such as on a flat roof, a fall arrest cart is the most convenient way to prevent catastrophic injury.
Fall arrest carts, such as those described in U.S. Pat. Nos. 8,240,431 and 6,227,553, generally include wheels and a braking system so that the mobile cart can be selectively moved into and held in position on an elevated surface, such as a flat rooftop.
The '431 patent further discloses an arrestor arm having an engagement plate that is movable between a disengaged position and an engaged position. In the disengaged position, the engagement plate is pivoted up and away from the elevated surface. In the engaged position, the engagement plate is pivoted into the elevated surface. A pulling force that is directly proportional to the weight of a person that has fallen and the velocity of the person's fall is excerpted on the arrestor arm to move the engagement plate from the disengaged position to the engaged position. An arm support excerpts a resistance force upon the arrestor arm to bias the engagement plate towards the disengaged position. Consequently, the pulling force must overcome the resistance force before the engagement plate will move towards the engaged position. Furthermore, as the engagement plate is moved towards the engaged position, and even when the engagement plate is in the engaged position, the resistance force biasing the engagement plate towards the disengaged position causes the net force biasing the engagement plate towards the engaged position to be less than the portion of the pulling force that biases the engagement plate towards the engaged position. Furthermore still, because the engagement plate pivots down towards the elevated surface, the portion of the pulling force that biases the engagement plate towards the engaged position is greater at the engaged position than it is at the disengaged position or even at an intermediate position when the engagement plate first comes into contact with the elevated surface.
Thus, it would be beneficial to have a mobile safety fall arrest cart that does not include an arm support. Furthermore, it would be beneficial to have a mobile safety fall arrest cart that does not excerpt a resistance force on an arrestor arm as an engagement plate pivots from a disengaged position to an engaged position, especially as the engagement plate is penetrating the elevated surface. Furthermore still, it would be beneficial if the mobile safety fall arrest cart includes a spike assembly having a spike member that does not pivot as the spike member makes contact with the elevated surface. Furthermore still, it would be beneficial if a portion of a pulling force that biases the spike assembly towards a final position was greatest while the spike member is moving to the final position rather than when the spike member is in the final position.